A variety of components in an internal combustion engine employ valves to control the flow of various fluids (e.g., pressurized air, fuel, lubricant, etc.). To increase the accuracy of valve positioning, and thus flow control, a valve may be actuated by a servomechanism that utilizes an electric motor and provides position feedback (e.g., via gearing). Valves employed in an internal combustion engine are frequently subjected to high temperatures and mechanical forces, both of which vary greatly throughout the course of engine operation. One example of such a valve is a wastegate valve whose position is varied to control an amount of exhaust gas reaching a turbine of a turbocharger. As the turbine may be mechanically coupled to a compressor configured to compress intake air, controlling exhaust flow via the wastegate valve facilitates control of the level of compression performed by the compressor, in turn controlling the boost pressure delivered to an associated engine. Wastegate valves are frequently subjected to high temperatures and mechanical forces due at least in part to the flow of proximate exhaust gas. Consequently, mechanical deformation in the wastegate may occur—for example, the length of a linkage coupling a wastegate actuator to the wastegate valve may increase due to thermal expansion. Despite the position feedback provided by employing a servomechanism to actuate the wastegate valve, valve positioning may become significantly inaccurate due to these thermal and mechanical factors. This may lead to inaccurate boost control, and in some examples, unintended collision of the wastegate valve with its end stop (e.g., valve seat) due to uncertainty in the location of the end stop, which can cause degraded wastegate operation.
German Pat. App. No. DE20121006532 describes a method of adapting wastegate valve positioning to thermal and mechanical factors that cause deformation in a wastegate. In particular, a fully closed position of the wastegate valve (i.e., the location of the valve end stop) is learned prior to engine startup and stored as a cold fully closed position. During subsequent engine operation, instances in which the wastegate valve is placed at the fully closed position are leveraged to learn the fully closed position during different thermal conditions—namely, at high temperatures. This fully closed position is stored as a hot fully closed position. The wastegate valve may then be positioned according to the fully closed positions learned for the cold and hot thermal conditions to thereby reduce inaccuracy introduced by thermal deformation.
The inventors herein have recognized an issue with the above approach. For many vehicles, opportunities that allow learning of the wastegate valve end stop following engine startup are rare. For some vehicles, such opportunities may be extremely limited even throughout their lifetimes. Moreover, commanded wastegate valve lifts that do not correspond to the end stop typically cannot be modified to correspond to the end stop to force an opportunity to learn the end stop—e.g., as surge may occur.
Methods for operating a wastegate are thus provided.
In one example, a method of controlling a linked valve actuator system comprises adjusting the actuator near an end stop based on a learned uncertainty end stop region, the region based on operating conditions.
In a more specific example, adjusting the actuator includes gradually moving the valve toward the end stop upon reaching an edge of the learned uncertainty end stop region.
In another aspect of the example, the operating conditions include desired boost, the gradual movement of the valve limited such that the desired boost is not unacceptably overshot.
In yet another aspect of the example, the operating conditions include a surge condition, the gradual movement of the valve limited according to the surge condition such that turbocharger compressor surge does not occur.
In still another aspect of the example, the learned uncertainty end stop region is based on one or more previously learned uncertainty end stop regions.
In still further another aspect of the example, a magnitude of the learned uncertainty end stop region is reduced as a number of previously learned uncertainty end stop regions increases.
In the examples described above, wastegate valve positioning may account for thermal and mechanical factors that alter the location of an end stop of the wastegate valve. Collisions between the valve and the end stop that may degrade wastegate valve operation may be avoided. Moreover, conducive operating conditions may be leveraged to reduce uncertainty in the location of the end stop. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.